A disc drive typically includes a base deck to which various components of the disc drive are mounted. A top cover cooperates with the base to form a housing that defines an internal, sealed environment for the disc drive. The components include a spindle motor, which rotates one or more discs at a constant high speed. Information is written to and read from tracks on the discs through the use of an actuator assembly. The actuator assembly includes actuator arms, which extend towards the discs, with one or more suspensions or flexures extending from each of the actuator arms. Mounted at the distal end of each of the flexures is a read/write head, which includes an air bearing slider enabling the head to fly in close proximity above the corresponding surface of the associated disc.
Disc drives are constructed in a clean room environment to prevent contaminants from entering the drive prior to the final assembly of the drive. Thus, the atmosphere within the assembled disc drive is typically that of the clean room, i.e., the filtered room air that is trapped within the drive once the cover is sealed to the base. While the seal between the base and the cover is sufficient to keep contaminants from entering the drive, it is possible for air and other gases to seep past (or permeate through) the seal and either enter or exit the drive. However, such small gas leaks are not an issue since most drives include a filtered port to equalize the air pressure within the drive to that of the ambient air pressure in order to prevent large stresses from being applied to the drive (such as during air shipment of the disc drive where the ambient air pressure is relatively low).
While air filled disc drives are currently prevalent, it is known that filling disc drives with low-density gases other than air (i.e., a gas such as helium having a lower density than air at similar pressures) can enhance drive performance. For example, helium (or another low density gas) can reduce the aerodynamic drag experienced by the spinning discs within the drive, thereby reducing the power requirements for the spindle motor. A helium filled drive thus uses substantially less power than a comparable disc drive that operates in an air environment. Additionally, the reduction in drag forces within the helium filled drive also reduces the amount of aerodynamic turbulence that is experienced by the drive components such as the actuator arms, the suspensions and the heads. These reductions in spindle motor power and “air” turbulence allow drives filled with low density gases to be operated at higher speeds than conventional air filled drives while maintaining the same tolerances (e.g., the same percentage of read/write errors). Additionally, helium filled drives may allow for higher storage capacities (i.e., higher recording densities) due to the fact that there is less turbulence within the drive and the heads may fly more closely to the disc surface.
Despite the advantages of helium filled drives, such drives have not been commercially successful. This is mainly due to problems associated with the helium (or other low density gas) leaking from the drives over time. Unlike air filled disc drives, helium filled drives do not include a filtered port to equalize the pressure within the drive to the ambient pressure. However, while prior art helium drives are completely sealed, it is still possible for the helium gas to leak out past the conventional rubber gasket seals used to seal the top cover to the drive base. Such leakage is not surprising given the relatively smaller size (lower atomic weight) of the helium atoms in comparison to the constituent gases found in air (i.e., nitrogen and oxygen). That is, the rubber gasket seals on prior art drives allow the relatively smaller helium atoms to diffuse through the rubber membrane. Indeed, such prior art gaskets do not provide hermetic seals with respect to air (i.e., the gaskets are also permeable to the larger atoms of nitrogen and oxygen in air) since it is air that typically displaces the helium gas that leaks from the drive.
As noted above, the prior art gasket seals are only intended to keep relatively large contaminants such as dust or smoke from the interior of the drive. Such gasket seals are preferred to other, more permanent methods of sealing a drive for two main reasons. First, the seals do not outgas and thus do not contribute to the contamination of the interior of the drive. Secondly, the seals may be reused if necessary during the assembly of the disc drive, such as when an assembled drive fails to pass certification testing and must be “reworked.” Reworking a drive typically entails removing the top cover from the base and replacing a defective disc or read/write head while the drive is still in the clean room environment. The reworked drive is then reassembled using the same rubber gasket positioned between the base and the top cover. Unfortunately, while such gasket seals are convenient, they simply do not provide a sufficient hermetic seal to maintain the required concentration of helium (or other low density gas) within the disc drive over the service life of the drive.
As helium leaks out of a disc drive and is replaced by air, the drive is subjected to undesirable operational effects possibly leading to failure of the drive. For example, the increased concentration of air may increase the turbulent forces on the drive heads due to the increased drag forces within the drive, and may further cause the heads to fly at too great a distance above the discs, thereby increasing the instances of read/write errors. The risk of unexpected failure due to inadequate amounts of helium is a considerable drawback to helium filled disc drives, particularly since the data stored within the disc drive can be irretrievably lost if the disc drive fails.
Accordingly there is a need for an improved disc drive that can effectively prevent helium (or another low density gas) from leaking out of the drive once the drive is finally assembled. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.